The Chinese mitten crab, Eriocheirsinensis, is an important farmed crustacean species in China, outranking other farmed crabs in yield and economic importance. An infection called “milky disease”, caused by the yeast, Metschnikowiabicuspidata, has emerged in E. sinensis farms in northeast China and has caused progressive economic losses. The diseased crabs present with opaque, whitish muscles and milky hemolymph. Currently, there are no effective drugs to treat the infection. Clarifying the transmission route of M. bicuspidata would help to treat and prevent the disease. We investigated the effects of three different M. bicuspidata infection methods (feeding, immersion, and cohabitation) on E. sinensis. All three infection methods led to a high infection rate in healthy crabs. After 35 d, the infection rate was 76.7%, 66.7%, and 53.3% in the feeding, immersion, and cohabitation groups, respectively. Diseased crabs exhibited the typical symptom of hemolymph emulsification, with a high pathogen load of M. bicuspidata. The yeast was not detected in the oocytes of infected crabs. Fertilized embryos, zoea larvae, and megalopae of infected ovigerous crabs tested negative for yeast, indicating that direct transmission from mother to offspring does not occur. Our results highlight avenues for the prevention and control of this yeast.

Torix tukubana is a poorly understood proboscidate leech species, generally an ectoparasite on amphibian species. In this study, the complete mitochondrial genome (mitogenome) of T. tukubana was sequenced using next-generation sequencing (NGS), and the essential characteristics, gene arrangement, and phylogenetic relationship were analyzed. The results showed that the T. tukubana mitogenome was 14,814 bp in length, consisting of 13 protein-coding genes (PCGs), 22 tRNAs, 2 rRNAs, and 1 control region (CR). The mitogenome composition presented a strong A + T bias (73.6%). All tRNAs had the typical clover structure except the trnS1 (TCT), whose dihydrouridine (DHU) arm was short, having only one complementary base pair. Additionally, 8 gene order patterns were identified among 25 known Hirudinea species, and T. tukubana was identical to the Hirudinea ground pattern. A phylogenetic analysis based on 13 PCGs indicated that all the studied species clustered into three main clades. The relationships among Hirudinea species were basically consistent with their gene arrangement results, but different from their morphological taxonomy. T. tukubana was in the monophyletic group of Glossiphoniidae, a finding consistent with previous research. Our results provided the essential characteristics of the T. tukubana mitogenome. As the first complete mitogenome of Torix, it could offer valuable information for a systematic understanding of the Hirudinea species.

Coastal wetlands are critical components of blue carbon ecosystems, yet the functional roles of benthic shellfish species in regulating sediment carbon dynamics are not yet fully elucidated. To address this knowledge gap, we investigated the effects of different shellfish zones—gastropods (Bullacta exarata, Umbonium thomasi) and bivalves (Mactra veneriformis, Meretrix meretrix, Potamocorbula laevis)—on sediment carbon fractions and microbial communities in representative intertidal wetlands of Liaodong Bay, China. We analyzed dissolved organic carbon (DOC), particulate organic carbon (POC), microbial biomass carbon (MBC), enzyme activities, and microbial genomic profiles, with particular emphasis on carbon fixation gene abundance within the top 0–10 cm of sediment. The results showed that POC and MBC levels in gastropod zones were 56.11% and 99.83% higher, respectively, than in bivalve zones, while carbon fixation gene abundance was 14.54% lower. Structural equation modeling (SEM) further revealed that shellfish type had a significant direct effect on MBC (λ = 0.824, p < 0.001). This study provides novel evidence that shellfish community composition regulates blue carbon storage through both biogeochemical and microbial pathways, highlighting the importance of species-specific management in shellfish aquaculture to enhance carbon sequestration. These findings offer a theoretical foundation for future assessments of coastal wetland carbon sinks and ecosystem service valuation.

“Milky disease” of the Chinese mitten crab (Eriocheir sinensis), caused by Metschnikowia bicuspidata, leads to substantial economic losses. Despite extensive research on its pathogenesis, the genetic basis of host resistance and underlying regulatory mechanisms remain unclear, limiting the development of disease-resistant varieties. This study aimed to (1) evaluate resistance differences among 10 E. sinensis families (five highly resistant and five sensitive) via artificial challenge; (2) identify disease-resistance-associated genetic loci using genome-wide association analysis (GWAS). Our findings revealed that the F05 family exhibited the strongest resistance, with a mortality rate of only 3% and a molting rate of 73%, accompanied by superior growth performance. Whole-genome resequencing identified 10,161,545 high-quality SNPs, and GWAS detected 767 loci significantly associated with disease-resistance traits, among which two pleiotropic SNPs (Chr46:18395778 and Chr1:20680490) were simultaneously associated with both “dead or not” and “qPCR fixed amount of fungi”, reflecting their functional relevance in regulating survival and pathogen load. Notably, we propose for the first time that E. sinensis achieves resistance by inducing M. bicuspidata into a viable but nonculturable (VBNC) state, in which the fungal cells remain metabolically active but cannot form colonies on conventional culture media. This study establishes a multidimensional resistance evaluation system, clarifies the genetic basis and novel mechanism of resistance, and provides valuable molecular markers for marker-assisted breeding. The findings contribute to reducing disease-related losses and promoting sustainable development of the E. sinensis aquaculture industry.